1. Field of the Invention
The present invention relates to a transparent thermoplastic film and a method of producing the transparent thermoplastic film capable of reducing the irregularity generated at the time of displaying black even when a liquid crystal display panel to which the transparent thermoplastic film is mounted is used at high temperature.
2. Description of the Related Art
In the past, there was carried out a method in which a transparent thermoplastic resin such as a cellulose acylate is formed to a film, stretched, and used as a retardation film of a liquid crystal display device in order to widen the viewing angle. In particular, recently, a retardation film is being developed by stretching a film which is formed by the use of a film melt-forming method which allows controlling equipment investment to be lowered. A method of forming such retardation film is described in Japanese Patent Laid-open Publication (herein after, abbreviated as “JP-A”) No. 2005-300978. The method is to give the retardation film specific values of retardation and haze, and to achieve widening of the viewing angle by building the film into a liquid crystal display device having a big screen. However, these liquid crystal display devices are easily affected by the environment and unevenness are appeared on the screen thereof when the setting environment is varied from the high temperature (for example, 50° C.), therefore, there is a demand of being improved. The unevenness on the screen is not ably shown when the screen is displaying black. That is, since an optical property of the retardation film used in the liquid crystal display device is varied due to a variation in the environment, a leakage of light occurs and is shown as image unevenness.